This application relates to communication systems and techniques including wireless communication systems and techniques.
Information may be represented by digital data bits and such data bits can be transmitted as data packets from a sender to one or multiple receivers. The transmission of such data bits may be made through various transmission links such as wired links (e.g. electrical cables and optical fibers) and wireless links (e.g., radio-frequency, microwave, or optical signals through air). Any perturbation between a sender and a receiver may adversely affect the signal and the data bits carried in the signal. Hence, the received data bits may be corrupted due to various perturbations during the transmission.
Various techniques may be used to reduce the errors in received data bits at a receiver. For example, the data bits from the sender may be encoded with redundancy bits for correcting bit errors prior to transmission and the encoded data bits are then transmitted to the receiver. The receiver decodes the received data bits, corrects any bit errors that may have occurred during the transmission based on the redundancy data bits, and retrieves the original data bits. The forward error correction (FEC) is a well-known implementation of this approach.
As another example, the receiver may check the bit errors in the received data bits and send a request for re-transmission to the sender if the data bits are corrupted. In this approach, the receiver may combine data bits of different transmissions by the sender to reduce the bit errors. In wireless communication systems, the automatic repeat request (ARQ) and hybrid ARQ (H-ARQ) are two implementation of this approach.
Different data combing techniques may be applied in H-ARQ in wireless communications. One example of the data combining techniques is the incremental redundancy (IR) retransmission where the data bits and some redundancy bits are transmitted first and the additional redundancy bits are incrementally transmitted subsequently upon requests by a receiver. The wireless air interfaces under IEEE P802.16-REVd/D5 (May 2004) provides an optional H-ARQ that uses the IR retransmission. The sections 6.3.17, MAC support for HARQ, in IEEE P802.16-REVd/D5 is incorporated herein by reference as part of the specification of this application. Jaehee Cho et al. of Samsung Electronics in their publication of “New FEC structure suitable for CTC and mobile Cellular Operation of 802.16 OFDMA” on Mar. 11, 2004 described an implementation of the IR retransmission for OFDM/OFDMA wireless systems and is incorporated herein by reference as part of the specification of this application.
Another example of the data combining techniques is the chase combining (CC) retransmission where an identical duplicate of a previously transmitted data packet which is detected to have errors by a receiver is sent for the second or more times so that the receiver can combine the received duplicates to improve the signal quality prior to decoding. Section 8.495 under IEEE C802.16e-04/136 describes an implementation of CC retransmission in OFDM/OFDMA systems and is incorporated herein by reference as part of the specification of this application.